I Can’t Sleep - Stainless Steel | Calm Bedtime Reading for Sleep

Episode Date: November 30, 2023

Drift off with this calm bedtime reading as Benjamin explores the story of stainless steel, helping you relax and find relief from insomnia. You’ll learn how this durable material was developed, the science behind its resistance to rust, and the many ways it is used in everyday life. Benjamin’s soothing cadence turns technical details into peaceful storytelling that reduces stress and quiets the mind. This is not whispering or hypnosis—just gentle, fact-filled narration designed to guide you toward rest. Press play, settle in, and let stainless steel bring you peaceful sleep. Want More? Request a Topic: https://www.icantsleeppodcast.com/request-a-topic Ad-Free Episodes: https://icantsleep.supportingcast.fm/ Shop Sleep-Friendly Products: https://www.icantsleeppodcast.com/sponsors Join the Discussion on Discord: https://discord.gg/myhGhVUhn7 This content is derived from the Wikipedia article on Stainless Steel, available under the Creative Commons Attribution-ShareAlike (CC BY-SA) license. Read the full article: Wikipedia – Stainless Steel. Happy sleeping! Learn more about your ad choices. Visit megaphone.fm/adchoices

You're listening to a Glassbox media podcast. What if I told you that most of the modern day self-help advice you've been hearing could actually make you worse? The key to a better life isn't about feel-good gimmicks that sound catchy. The Mentally Stronger Podcast gives you access to a licensed therapist who shares science-backed tools that will actually change your life. Hi, I'm Amy Morin, psychotherapist, mental strength trainer, and international best-selling author. In each episode, we cover research-back strategies, like how to stop relying on willpower and start creating habits for lasting change. And the five mental strength-building exercises you can do from your couch. I also speak to world-class experts like Dr. Nicole Kane, who shares how to permanently heal anxiety by addressing the root cause.

With over 200 episodes in our catalog, this podcast is for you if you're ready to crush self-doubt, conquer challenges, become stronger than ever with therapist-approved strategies that can change your life. Listen to Mentally Stronger with Therapist Amy Morin, wherever you get your podcasts. Welcome to the I Can't Sleep podcast, where I read random articles from across the web to bore you to sleep with my soothing voice. I'm your host, Benjamin Boster. Today's episode is from a Wikipedia article titled Stainless Steel. Stainless Steel also known as Inox, corrosion-resistant steel, and rustless steel, is an alloy of iron that is resistant to rusting in corrosion. It contains at least 10.5% chromium and usually nickel, and may also contain other elements, such as carbon, to obtain the desired properties.

Stainless steel's resistance to corrosion results from the chromium, which forms a pattern. passive film that can protect the material and self-heal in the presence of oxygen. The alloy's properties such as luster and resistance to corrosion are useful in many applications. Stainless steel can be rolled into sheets, plates, bars, wire, and tubing. These can be used in cookware, cutlery, surgical instruments, major applications, vehicles, construction material and large buildings, industrial equipment, e.g. in paper mills, chemical plants, water treatment, and storage tanks and tankers for chemicals and food products.

The biological cleanability of stainless steel is superior to both aluminum and copper and comparable to glass. Its cleanability, strength, and corrosion resistance have prompted the use of stainless steel in pharmaceutical and food processing plants. Different types of stainless steel are labeled with an AISI-3-digit number. The ISO-15510 standard lists the chemical compositions of stainless steels of the specifications in existing ISO, ASTM, E-N, J-I-S, and G-B standards. in a usable interchange table.

Although stainless steel does rust, this only affects the outer few layers of atoms, its chromium content shielding deeper layers from oxidation. The addition of nitrogen also improves resistance to pitting corrosion and increases mechanical strength. Thus, there are numerous grades of stainless steel with varying chromium and molybdenum contents to suit the environment the alloy must endure.

Corrosion resistance can be increased further by the following means. Increasing chromium content to more than 11%, adding nickel to at least 8%, adding molybdenum, which also improves resistance to pitting corrosion. Stainless steel is strong, about three times stronger than ordinary steel. For type AISI-302 cold rolled, its yield strength, i.e. its elastic limit, is 520 megapax scales, and its ultimate strength is 860 megapa scales. It's also quite hard. Its hardness on the Brunel scale is 200, versus 120 for ordinary steel, and 15 for pure aluminum.

On the most scale, its hardness is eight, comparable to that of pure chromium at 8.5 brinnell hardness, or quartz, at seven brinnell hardness. Stainless steel is a steel, and as such its melting point is near that of ordinary steel, and much higher than the melting points of aluminum or copper. As with most alloys, the melting point of stainless steel is expressed in the form of a range of temperatures and not a singular temperature. This temperature range goes from 1,400 to 1530 degrees Celsius, depending on the specific consistency of the alloy in question.

Like steel, stainless steels are relatively poor conductors of electricity, with significantly lower electrical conductivitys than copper. In particular, the non-electrical contact resistance, ECR of stainless steel, arises as a result of the dense protective oxide layer and limits its functionality in applications as electrical connectors. Copper alloys and nickel-coded connectors tend to exhibit lower ECR values and are preferred materials for such applications. Nevertheless, stainless steel connectors are employed in situations where ECR poses a lower design criteria and corrosion resistance is required. For example, in high temperatures and oxidizing

environments, martinzitic, duplex, and ferritic stainless steels are magnetic, while austinitic stainless steel is usually non-magnetic. Ferritic steel owes its magnetism to its body-centered cubic crystal structure, in which iron atoms are arranged in cubes, with one and iron atom at each corner and an additional iron atom in the center. This central iron atom is responsible for ferretic steel's magnetic properties. This arrangement also limits the amount of carbon the steel can absorb to around 0.025%. Grades with low coercive field have been developed for electrovalves used in household appliances and for injection systems in internal combustion engines.

Some applications require non-magnetic materials, such as magnetic resonance imaging. Austenitic stainless steels, which are usually non-magnetic, can be made slightly magnetic through work-hardening. Sometimes, if austinitic steel is bent or cut, magnetism occurs along the edge of the stainless steel. because the crystal structure rearranges itself. Galling, sometimes called cold welding, is a form of severe adhesive wear,

which can occur when two metal surfaces are in relative motion to each other and under heavy pressure. Austenitic stainless steel fasteners are particularly susceptible to thread galling, though other alloys that self-generate a protective oxide surface film, such as aluminum and titanium, are also susceptible. Under high-contact force sliding, this oxide can be deformed, broken, and removed from parts of the component, exposing the bare reactive metal. When the two surfaces are of the same material,

these exposed surfaces can easily fuse. Separation of the two surfaces can result in surface tearing and even complete seizure of metal components or fasteners. Galling can be mitigated by the use of dissimilar materials, bronze against stainless steel, or using different stainless steels, Martin Cidic against austinitic. Additionally, threaded joints may be looper,

to provide a film between the two parts and prevent calling. Nitronic 60, made by selective alloying with manganese, silicon, and nitrogen, has demonstrated a reduced tendency to gall. The density of stainless steel ranges from 7,500 kilograms per meter cubed to 8,000 kilograms per meter cubed depending on the alloy. The invention of stainless steel followed a series of scientific developments, starting in 1798 when chromium was first shown to the French Academy by Louis Vaccalan. In the early 1800s, British scientists James Stoddard, Michael Faraday, and Robert Mallet observed the resistance of chromium iron alloys, chromium steels, to oxidizing agents. Robert Bunsen discovered chromium's resistance to strong acids.

The corrosion resistance of iron chromium alloys may have been first recognized in 1821 by Pierre Berthier, who noted their resistance against attack by some acids and suggested their use in cutlery. In the 1840s, both Britain's Sheffield Steelmakers and then Krupp of Germany were producing chromium steel with the latter employing it for cannons in the 1850s. In 1861, Robert Forrester Moshe took out a patent on chromium steel in Britain. These events led to the first American production of chromium containing steel by Jay Bauer of the chrome steel works of Brooklyn for the construction of bridges. A U.S. patent for the product was issued in 1869. This was followed with recognition of the corrosion resistance of chromium alloys by Englishman John T. Woods and John Clark, who noted ranges of chromium from 5 to 30 percent with added tungsten and medium carbon.

They pursued the commercial value of the innovation via a British patent for weather-resistant alloys. In the late 1890s, German chemist Hans Goldschmidt developed an aluminum-thermic thermite process for producing carbon-free chromium. Between 1904 and 1911, several researchers, particularly Leon Guillaise of France, prepared alloys that would be considered stainless steel today. In 1908, the Essen firm Friedrich Kreb Germania Werft built the 300,000,000. 66-ton sailing yacht, Germania, featuring a chrome-nickel steel hole in Germany. In 1911, Philip Monards reported on the relationship between chromium content and corrosion resistance. On the 17th of October 1912, Krup engineers Benno Strauss and Edward Maurer patented

as Neurosta, the ostinitic stainless steel known today as 188 or A.I. ISI-Type 304. Similar developments were taking place in the United States, where Christian Donsis and General Electric and Frederick Beckett at Union Carbide were industrializing ferritic stainless steel. In 1912, Elwood Haynes applied for a U.S. patent on a martin-cidic stainless steel alloy, which was not granted until 1919. While seeking a corrosion-resistant alloy for gun barrels in 1912,

Harry Brearley of the Brown Firth Research Laboratory in Sheffield, England, discovered and subsequently industrialized a martin-cidic stainless steel alloy, today known as AISI Type 420. The discovery was announced two years later in a January 1915 newspaper article in the New York Times. The metal was later marketed under the Stay Bright brand by Firth Vickers in England and was used for the new entrance canopy for the Savoy Hotel in London in 1929. Rarely applied for a U.S. patent during 1915 only to find that Haynes had already registered one. Rarely and Haynes pooled their funding, and with a group of investors formed the American Stainless Steel Corporation,

with headquarters in Pittsburgh, Pennsylvania. Brerley initially called this new alloy rustless steel, The alloy was sold in the U.S. under different brand names like Allegheny metal and Neurosta Steel. Even within the metallurgy industry, the name remained unsettled. In 1921, one trade journal called it unstable steel. Barely worked with a local cutlery manufacturer who gave it the name stainless steel. As late as 1932, Ford Motor Company, continued calling the alloy rustless steel in automobile promotional materials.

In 1929, before the Great Depression, over 25,000 tons of stainless steel were manufactured and sold in the U.S. annually. Major technological advances in the 1950s and 1960s allowed the production of large tonnages at an affordable cost. AOD process argon oxygen decarbonization for the removal of carbon and sulfur, continuous casting and hot strip rolling, the Z-Mill or Sendzimmer cold rolling mill, the Crusoe-L-L-U, and related processes which use steam instead of some or all of the argon. Stainless steel is classified into five main families that are primarily differentiated by their crystalline structure. austinitic ferritic

martin-sidic duplex precipitation hardening austinitic austinitic austinic stainless steel is the largest family of stainless steel making up about two-thirds of all

stainless steel production they possess an austinitic microstructure which is a face-centered cubic crystal structure this microstructure is achieved by allowing steel with sufficient nickel and or manganese and nitrogen to maintain an austinitic microstructure at all temperatures, ranging from the cryogenic region to the melting point. Thus, austinic stainless steels are not hardenable by heat treatment since they possess the same microstructure

at all temperatures. However, forming temperature is an essential factor for metastable austinic stainless steel. Products to accommodate microstructures and cryogenic mechanical performance. Metastable austinic stainless steels are widely used in manufacturing cryogenic pressure vessels, CPVs, owing to their high cryogenic toughness, ductility, strength, corrosion resistance, and economy. Cryogenic cold forming of austinic stainless steel is an extension of the heating, quenching tempering cycle, where the final temperature of the material before full load use is taken down to a cryogenic temperature range. This can remove residual stresses and improve wear resistance. Hostenitic stainless steel subgroups, 200 series and 300 series, 200 series are chromium

magnanease nickel alloys that maximize the use of manganese and nitrogen to minimize the use of nickel. Due to their nitrogen addition, they possess approximately 50% higher yield strength than 300 series stainless sheets of steel. Type 201 is hardenable through cold working. Type 202 is general purpose stainless steel, decreasing nickel content and increasing manganese results in weak erosion resistance. 300 series are chromium nickel alloys that achieve their austinetic microstructure almost exclusively by nickel allowing. Some very high alloy grades include some nitrogen to reduce nickel requirements. 300 series is the largest group and the most widely used. Type 304 is the most common. It also is known as 188 and 1810 for its composition of 18% chromium and 8% or 10% nickel

respectively. Type 316 is the second most common austinitic stainless steel. The addition of 2% molybdenum provides greater resistance to acids and localized corrosion caused by chloride ions. Low-carbon versions, such as 316L or 304L, have carbon contents below 0.03% and are used to avoid corrosion problems caused by welding. Ferritic. Ferritic stainless steels possess a ferrite microstructure like carbon steel, which is a body-centered cubic crystal structure, and contain between 10.5% and 27% chromium, with very little or no nickel.

This microstructure is present at all temperatures due to the chromium addition, so they are not capable of being hardened by heat treatment. They cannot be strengthened by cold work to the same degree as austinitic stainless steels. They are magnetic. Additions to niobium N.B. N.B. Titanium, Ti, and Zr. To type 430, allow good weldability. Due to the near absence of nickel,

they are less expensive than austinitic steels and are present in many products, which include automobile exhaust pipes type 409 and 409 CB are used in North America. Stabilized grades type 439 and 441 are used in Europe. Architectural and structural applications, type 430, which contains 17% CR, building components such as slate hooks, roofing, and chimney ducts, power plates in solid oxide fuel cells operating at temperatures around 700 degrees Celsius. Martin Cidic Martin Cidic stainless steels have a body-centered cubic crystal structure and offer a wide range of properties and are used as stainless steel engineering steels, stainless tool seals, and creep re-centred. resistant steels. They are magnetic and not as corrosion-resistant as ferritic and

austenitic stainless steels due to their low chromium content. They fall into four categories with some overlap. F-E-C-R-C-C-grades. These were the first grades used and are still widely used in engineering and wear-resistant applications. F-E-C-R-N-I-C-C-G grades. Some car Carbon is replaced by nickel. They offer higher toughness and higher corrosion resistance. Grade E.N. 1.4303 casting grade CA6N. with 13% CR and 4% NI is used for most Pelton, Kaplan, and Francis turbines and hydroelectric power plants. Because it has good casting properties, good weldability, and good resistance to cavitation erosion. Precipitation hardening grades

Grade E.N. 1.4542, also known as 17-4 pH, the best-known grade, combines martin-cidic hardening and precipitation hardening. It achieves high strength and good toughness and is used in aerospace, among other applications. creep-resisting grades. Small additions of niobium, vanadium, boron, and cobald increase the strength and creep-resistance up to about 650 degrees Celsius.

Martin Cidic stainless steels can be heat-treated to provide better mechanical properties. The heat treatment typically involves three steps. One, hostinitizing, in which the steel is heated to a temperature in the range of 980, to 150 degrees Celsius depending on grade. The resulting ostinite has a face-centered cubic crystal structure. 2. Quenching. The ostinite is transformed into martin-site, a hard-body-centered tetragonal crystal structure.

The quenched martin-site is very hard and too brittle for most applications. Some residual austinite may remain. Tempering. Martin site is heated to around 500 degrees Celsius held at temperature, then air cooled. Higher tempering temperatures decrease yield strength and ultimate tensile strength, but increase the elongation and impact resistance. Replacing some carbon in martinitic stainless steels by nitrogen is a recent development. Limited solubility of nitrogen is increased by the,

the pressure electroslag refining PESR process, in which melting is carried out under high nitrogen pressure. Steel containing up to 0.4% nitrogen has been achieved, leading to higher hardness and strength and higher corrosion resistance. As PESR is expensive, lower but significant nitrogen contents have been achieved using the standard AOD process. Duplex

Duplex stainless steels have a mixed microstructure of austinite and ferrite, the ideal ratio being a 50-50 mix, though commercial alloys may have ratios of 40-60. They are characterized by higher chromium 19 to 32%, and molybdenum up to 5%, and lower nickel contents than austinic stainless steels. Duplex stainless steels have roughly twice the yield strength of austinic stainless steel. Their mixed microstructure provides improved resistance to chloride stress corrosion cracking in comparison to austinic stainless steel types 304 and 316. Duplex grades are usually divided into three subgroups based on.

on their corrosion resistance. Lane duplex, standard duplex, and super duplex. The properties of duplex stainless steels are achieved with an overall lower alloy content than similar performing super austinitic grades, making their use cost effective for many applications. The pulp and paper industry was one of the first to extensively use duplex stainless steel. Today, the oil and gas industry is the largest user and has pushed for more corrosion-resistant grades

leading to the development of super-duplex and hyper-duplex grades. More recently, the less expensive and slightly less corrosion-resistant lean-duplex has been developed, chiefly for structural applications in building and construction, concrete reinforcing bars, plates for bridges, coastal works, and in the water industry. Precipitation hardening Precipitation hardening stainless steels have corrosion resistance comparable to hostenitic varieties, but can be precipitation hardened to even higher strengths than other martinitic grades.

There are three types of precipitation hardening stainless steels. Martin Cidic, 17 to 4 pH. Contains about 17% CR, 4% N.I, 4% CU, and 0.3% NB. Solution treatment at about 1,040 degrees Celsius, followed by quenching results in a relatively ductile martinitic structure. Subsequent aging treatment at 475 degrees Celsius, precipitates NB and C.U. rich phases that increased the strength up to above 1,000 megapascal yield strength. This outstanding strength level is used in high-tech applications

such as aerospace, usually after remelting to eliminate non-metallic inclusions, which increases fatigue life. Another major advantage of this steel is that aging, unlike tempering treatments is carried out at a temperature that can be applied to nearly finished parts without distortion and discoloration. Semi-Austenitic 17 to 7 pH contains about 17% CR, 7.2% N.I and 1.2% AL. Typical heat treatment involves solution treatment and quenching. At this point, the structure remains austinitic. Martin Zitic transformation is then obtained either by a cryogenic treatment at negative 75 degrees Celsius or by severe cold work, over 70% deformation, usually by cold rolling or wire

drawing. Aging at 510 degrees Celsius, which precipitates the NI3 AI intermetallic phase, is carried out as above on nearly finished parts. Yield stress levels above 1400 megapast scales are then reached. Austenitic A286 contains about CR 15%, NI 25%, T.I.2.1%, MO1.2%, V1.1.3% and B.005%. The structure remains austinitic at all temperatures. Typical heat treatment involves solution treatment and quenching,

followed by aging at 750 degrees Celsius. Aging forms N.I.3TI precipitates and increases the yield strength to about 650 megapx scales at room temperature. Unlike the above grades, the mechanical properties increase resistance of the state steel remain very good at temperatures up to 700 degrees Celsius. As a result, A286 is classified as an FE-based super alloy used in jet engines, gas turbines, and turbo parts. Grades. Over 150 grades of stainless steel are recognized, of which 15 are the most widely used.

Many grading systems are in use, including U.S. S-A.E. Steel grades. The unified numbering system for metals and alloys, UNS, was developed by the ASTM in 1970. The Europeans have adopted EN1088, corrosion resistance. Unlike carbon steel, stainless steels do not suffer uniform corrosion when exposed to wet environments. Unprotected carbon steel rusts readily when exposed to a combination of air and moisture. The resulting iron oxide surface layer is porous and fragile. In addition, as iron oxide occupies a larger volume than the original steel, this layer expands and tends to flake and fall away,

exposing the underlying steel to further attack. In comparison, stainless steels contain sufficient chromium to undergo passivation, spontaneously forming a microscopically thin innered surface film of chromium oxide by reaction with the oxygen in the air and even the small amount of dissolved oxygen in the water. This passive film prevents further corrosion by blocking oxygen diffusion to the steel surface and thus prevents corrosion from spreading into the bulk of the metal. This film is self-repairing, even when scratched or temporarily disturbed. by an upset condition in the environment that exceeds the inherent corrosion resistance of that grade.

The resistance of this film to corrosion depends upon the chemical composition of the stainless steel, chiefly the chromium content. It is customary to distinguish between four forms of corrosion, uniform, localized, pitting, Galvinick, and SCC stress corrosion cracking. Any of these forms of corrosion can occur when the grade of stainless steel is not suited for the working environment. The designation Cress refers to corrosion-resistant stainless steel. Uniform corrosion takes place in very aggressive environments, typically where chemicals are produced or heavily used, such as in the pulp and paper industries.

The entire surface of the steel is attacked. and the corrosion is expressed as corrosion rate in millimeters per year. Usually less than 0.1 millimeter per year is acceptable for such cases. This is typically the case when stainless steels are exposed to acidic or basic solutions. Whether stainless steel corrodes depends on the kind and concentration of acid or base and the solution temperature. Uniform corrosion is typically easy to avoid because of extensive published corrosion data or easily performed laboratory corrosion testing.

Acidic solutions can be put into two general categories, reducing acids such as hydrochloric acid and dilute sulfuric acid, and oxidizing acids, such as nitric acid and concentrated sulfuric acid. increasing chromium and molybdenum content provides increased resistance to reducing acids, while increasing chromium and silicon content provides increased resistance to oxidizing acids. Sulfuric acid is one of the most produced industrial chemicals. At room temperature, type 304 stainless steel is only resistant to 3% acid, while Type 316 is resistant to 3% acid up to 50 degrees Celsius

and 20% acid at room temperature. Thus, Type 304S is rarely used in contact with sulfuric acid. Type 904L and alloy 20 are resistant to sulfuric acid at even higher concentrations above room temperature. Concentrated sulfuric acid possesses oxygen. oxidizing characteristics like nitric acid, and thus silicon-bearing stainless steels are also useful. Hydrochloric acid damages any kind of stainless steel and should be avoided. All types of stainless steel resist attack from phosphoric acid and nitric acid at room temperature.

At high concentrations and elevated temperatures, attack will occur and higher alloy stainless steels are required. In general, organic acids are less corrosive than mineral acids, such as hydrochloric and sulfuric acid. Type 304 and type 316 stainless steels are unaffected by weak base, such as ammonium hydroxide, even in high concentrations and at high temperatures. The same grades exposed to stronger bases such as sodium hydroxide at high concentrations and high temperatures will likely experience some etching and cracking. Increasing chromium and nickel contents provide increased resistance. All grades resist damage from aldehydes and amines,

though in the latter case type 316 is preferable to type 304. Cellulose acetate damages type 304 unless the temperature is kept low. Fats and fatty acids only affect type 3.3. 304 at temperatures above 150 degrees Celsius and type 316 SS above 260 degrees Celsius, while type 317 SS is unaffected at all temperatures. Type 316L is required for the processing of urea. Localized corrosion can occur in several ways, e.g. pitting corrosion and crevice corrosion.

These localized attacks are most common, in the presence of chloride ions. Higher chloride levels require more highly alloyed stainless steels. Localized corrosion can be difficult to predict because it is dependent on many factors, including chloride ion concentration. Even when chloride solution concentration is known, it is still possible for localized corrosion to occur unexpectedly. Chloride ions can become unevenly concentrated in certain areas, such as in crevices, e.g. under gaskets, or on surfaces in vapor spaces due to evaporation and condensation.

Temperature. Increasing temperature increases susceptibility. Acidity. Increasing acidity increases susceptibility. Stagnation. Stagnation. Stagnantin condition. increase susceptibility. Oxidizing species. The presence of oxidizing species such as ferric and cupric ions increases susceptibility. Pitting corrosion is considered the most common form of localized corrosion. Stress corrosion cracking, SCC, is a sudden cracking and failure of a component without deformation. It may occur when three conditions are met. The part is stressed by an applied load or by residual stress.

The environment is aggressive, high chloride level, temperature above 50 degrees Celsius. The stainless steel is not sufficiently SEC resistant. The SEC mechanism results from the following sequence of events. 1. Pitting occurs. 2. Cracks start from a pit initiation site. 3. Cracks then propagate. through the metal in a trans-granular or inter-granular mode, for failure occurs. Whereas pitting usually leads to unsightly surfaces, and at worst, to perforation of the stainless sheet,

failure by SEC can have severe consequences. It is therefore considered as a special form of corrosion. As SEC requires several conditions to be met, it can be counteracted with relative easy measures, including reducing the stress level, the oil and gas specifications provide requirements for maximal stress level in H2S containing environments. Assessing the aggressiveness of the environment, high chloride content, temperature above 50 degrees Celsius, etc. Selecting the right type of stainless steel, superostenitic, such as grade 904L, or super duplex, ferritic stainless steels and duplex stainless steels are very resistant to SCC. Galvanic corrosion, also called dissimilar metal corrosion, refers to corrosion damage induced

when two dissimilar metals are coupled in a corrosive electrolyte. The most common electrolyte is water, ranging from freshwater to seawater. When a galvanic couple forms, one of the metals and the couple becomes the anode and corrods faster than it would alone, while the other becomes the cathode and corrods slower than it would alone. Stainless steel, due to having a more positive electrode potential than, for example, carbon steel and aluminum, becomes the cathode, accelerating the corrosion of the anotic metal. An example is the corrosion of aluminum rivets fastening stainless steel sheets in contact with water. The relative surface areas of the anode and the cathode are important in determining the rate of corrosion.

In the above example, the surface area of the rivets is small compared to that of the stainless steel sheet, resulting in rapid corrosion. However, if stainless steel fasteners are used to assemble a luller, aluminum sheets, galvanic corrosion will be much slower because the galvanic current density on the aluminum surface will be many orders of magnitude smaller. A frequent mistake is to assemble stainless steel plates with carbon steel fasteners, whereas using stainless steel to fasten carbon steel plates is usually acceptable. The reverse is not.

Providing electrical insulation between the dissimilar metals, where possible, is effective at preventing this type of corrosion. At elevated temperatures, all metals react with hot gases. The most common high-temperature gaseous mixture is air, of which oxygen is the most reactive component. To avoid corrosion in air, carbon steel is limited to approximately 480 degrees Celsius. Oxidation resistance in stainless steels increases

with additions of chromium, silicon, and silicon, and oil. aluminum. Small additions of serium and itrium increase the adhesion of the oxide layer on the surface. The addition of chromium remains the most common method to increase high temperature corrosion resistance in stainless steels. Chromium reacts with oxygen to form a chromium oxide scale, which reduces oxygen diffusion into the material. The minimum 10.5% chromium and stainless steels provides resistance to approximately 700 degrees Celsius, while 16% chromium provides resistance up to approximately 1,200 degrees Celsius. Type 304, the most common grade of stainless steel with 18% chromium,

is resistant to approximately 800 degrees Celsius. Other gases such as sulfur dioxide, hydrogen sulfide, carbon monoxide, chlorine, also attack stainless steel. Resistance to other gases is dependent on the type of gas, the temperature, and the alloying content of the stainless steel. With the addition of up to 5% aluminum, ferritic grades, F-E-C-R-A-L are designed for electrical resistance and oxidation resistance at elevated temperatures. Such alloys include canthal produced in the form of wire or ribbons. Standard mill finishes can be applied to flat rolled stainless steel directly by the rollers and by mechanical abrasives. Steel is first rolled to size and thickness and then annealed to change the properties of the final material.

Any oxidation that forms in the surface mill scale is removed by pickle, and a passive layer is created on the surface. A final finish can then be applied to achieve the desired aesthetic appearance. The following designations are used in the U.S. to describe stainless steel finishes by ASTM, A480-A480M-18. Number 0. Hot rolled, annealed, thicker plates. number 1 1d hot rolled annealed and passivated number 2d cold rolled annealed and passivated number 2d cold rolled annealed pickled and passivated number 2 b same as above with additional pass through highly polished rollers number 2 b a 2 r bright an eel b a or 2 r same as above as above then bright and yield under oxygen-free atmospheric condition.

Number 3. G, 2G. Coarse abrasive finish applied mechanically. Number 4. 1J, 2J, brushed finish. Number 5, satin finish. Number 6, 1K, 2K, matte finish, brushed but smoother than number 4. Number 7, 1p, 2p, reflective finish. Number 8, mirror finish. Number 9, bead blast finish.

Number 10, heat-colored finish, offering a wide range of electro-polished and heat-colored surfaces.